Organic esters of carbonic acid, particularly cyclic alkylene carbonates such as propylene carbonates and ethylene carbonates, are known hydraulic cement set accelerating agents. Such agents decrease the time necessary to harden a cementitious composition comprised of water, hydraulic cement, and other optional components such as aggregate. The use of carbonic acid esters for such purpose is described in detail in JP 58-135166 (Chemical Abstracts, Vol. 100, No. 2, 1983, Abstract No. 11845p), JP 61-247648 (Chemical Abstracts, Vol. 106, No. 22, 1987, Abstract No. 181621d), and U.S. Pat. No. 5,453,123. The last named patent additionally teaches that carbonic acid esters function as thixotropic additives in cementitious compositions. That is, carbonic acid esters have a thixotropic effect if incorporated into a mixture of hydraulic cement and water.
Many carbonic acid esters, however, are liquids or low melting solids which hydrolyze rapidly when placed in contact with water in a highly acidic or basic environment. In many end-use applications such as grout or concrete repair, cement is sold in dry, bagged form and simply mixed with water immediately before use at the construction or repair site. Adding the carbonic acid ester set-accelerating agent together with the water at the time of mixing is technically possible, but not favored because of the problems associated with securing and maintaining a separate supply of the carbonic acid ester and adding the correct dosage to the cementitious composition. Most end-users of bagged cement products are not currently prepared to handle liquid or low-melting organic admixtures. Premixing the carbonic acid ester with the dry cement may also be problematic due to the fact that the cement, which is highly basic in character, may tend to catalyze the premature decomposition of the carbonic acid ester during the time the bagged cement pre-mix is stored (particularly if the pre-mix is exposed to moisture). An alternative method of handling the carbonic acid ester would be in the form of concentrated aqueous solutions or dispersions, which could then be combined with the dry cement and water at the construction site. However, many carbonic acid esters such as propylene carbonate have limited solubility in water. Maintaining stable dispersions of the carbonic acid ester during storage may also be difficult.